1. Field of Invention
The invention relates to a piezoelectric ink-jet printhead that is flat in shape and to a manufacturing method of the same.
2. Description of Related Art
U.S. Patent Publication No. 2001/0020968 and Japanese Laid-Open Patent Publication No. 2002-36545, both of which are incorporated herein by reference, disclose an on-demand type ink-jet printhead having a cavity unit and a piezoelectric actuator. The cavity unit is formed by stacking a plurality of manifold plates under a base plate having pressure chambers, by placing a nozzle plate at the bottom of the manifold plates, and by bonding theses plates using an adhesive. The piezoelectric actuator in the form of a flat plate is bonded to the upper surface of the base plate of the cavity unit such that piezoelectric elements of the piezoelectric actuator face the pressure chambers formed in the base plate.
With this structure, the piezoelectric actuator and the cavity unit are arranged to overlap each other within the area of the ink-jet printhead in the plan view thereof. Thus, the ink-jet printhead is advantageously made compact.
With this structure, however, because the cavity unit is formed by laminating a plurality of metal plates while the piezoelectric actuator is formed by laminating a plurality of ceramic sheets, the cavity unit expands more than the piezoelectric actuator does when they are thermally bonded. The cavity unit and the piezoelectric actuator are bonded by applying a thermosetting adhesive, such as epoxy resin, therebetween and by heating. When the piezoelectric actuator and the cavity unit are cooled down after the adhesive is hardened to fix the piezoelectric actuator to the upper surface of the cavity (surface with pressure chambers), contraction of the cavity unit is restricted on its upper surface because the piezoelectric actuator having a low linear expansion coefficient is bonded thereto. On the other hand, the cavity unit contracts greatly on its lower surface (surface with nozzles). As a result, the cavity unit is concavely curved on the nozzle side. Conversely, the cavity unit is convexedly curved on the piezoelectric actuator side. Such concave curving is remarkable in the longitudinal direction of the cavity unit, that is, in the direction of the nozzle array. Because ink is ejected in a direction perpendicular to the curved lower surface of the cavity unit, the quality of an image formed on a recording sheet may be degraded.